RNA sequencing identifies specific PIWI-interacting small non-coding RNA expression patterns in breast cancer

PIWI-interacting RNAs (piRNAs) are a novel class of small ncRNAs initially isolated from germ line cells; although recent studies report that they are expressed also in somatic cells. To elucidate the role of piRNAs in somatic cells, in particular from breast cancer, we performed the first extensive next generation sequencing expression analysis of small RNA transcriptomes of hormone responsive breast cancer cell lines in different culture conditions. In addition, to understand the behavior of piRNAs with respect to miRNAs in breast tumor tissues, small RNA sequence data set available in Gene Expression Omnibus (GSE39162) database was used. Results led to the identification of ~100 and ~150 human piRNAs in the breast cancerous cell lines and tumors respectively, several of which differentially expressed in cell lines under different experimental conditions tested or in response to ERß and in tumor tissues. Western blotting and Q-PCR analysis also revealed the presence in breast cell lines of PIWIL (PIWI Like) subfamily members proteins encoded in the human genome (PIWIL2/HILI and PIWIL4/HIWI2) and of other components of the piRNA biogenesis pathways, suggesting that this might indeed be functional in somatic cells. These results show that piRNAs are expressed in human somatic cells, in particular in cancer, where their expression is influenced by neoplastic transformation, growth conditions and estrogen receptor beta. More important, we demonstrate for the first time a distinct pattern of piRNAs expression in cancerous vs normal breast tissues, which suggests a potential role of these epigenetic modulators in mammary carcinogenesis and maintenance of the cancer cell phenotype. Overall design: In addition, to understand the behavior of piRNAs with respect to miRNAs in breast tumor tissues, small RNA sequence data set available in Gene Expression Omnibus (GEO; GSM957192 TAX577740T ,GSM957194 TAX577740N, GSM957195 TAX577453T, GSM957197 TAX577453N, GSM957198 TAX577745T, GSM957200 TAX577745N, GSM957201 TAX577579T, GSM957203 TAX577579N) was used.

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Hashim A, Rizzo F, Marchese G, Ravo M, Tarallo R, Nassa G, Giurato G, Santamaria G, Cordella A, Cantarella C, Weisz A